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Radiation-Dynamics Effects in Reactors Safety

#2228


Radiation-Dynamic Effects at Irradiation with Neutrons, Ions, Fission Fragments, Non-traditional Methods of Material Properties Modification and the Problem of Nuclear Reactors Safety

Tech Area / Field

  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors
  • FIR-MAT/Materials/Fission Reactors

Status
3 Approved without Funding

Registration date
22.06.2001

Leading Institute
Institute of Electrophysics, Russia, Sverdlovsk reg., Ekaterinburg

Supporting institutes

  • VNIITF, Russia, Chelyabinsk reg., Snezhinsk\nUral Branch of RAS / Institute of Metal Physics, Russia, Sverdlovsk reg., Ekaterinburg

Collaborators

  • Forschungszentrum Rossendorf / Institut für Ionenstrahlphysik und Materialforschung, Germany, Dresden\nHahn-Meitner Institut Berlin, Germany, Berlin\nSRI International / Materials Research Laboratory, USA, CA, Menlo Park\nUniversite de Rouen / Faculte des Sciences et Techniques, France, Saint Etienne du Rouvray

Project summary

Project main objective.

The Project objective is the experimental and theoretical investigation of radiation-dynamic (RD) effects: irradiation-induced fast processes and phase transformations externally similar to combustion and detonation phenomena, observed at irradiation with neutrons, fission fragments and heavy ions in metastable metals and alloys, including radiation-resistant steels from the standpoint of nuclear reactors safety and development of basically new radiation methods of material modification. The unique research nuclear reactors, ion accelerators and analytical techniques available to the participating institutions will be used.

Background and Introduction.

Radiation-dynamic (RD) transformations are initiated at the front of a microshock wave caused by the evolution of dense cascades of atomic collisions (see, e.g.: 1. Zhukov V., Ryabenko A., Radiation Effects, 1984, v.82, 85-95; 2. Zhukov V.P., Demidov A.V. Atomnaya energiya, 1985, v.59, B1, pp. 29-33; 3. Ovchinnikov V.V. Proc. XVI ISDEIV. Moscow-St.Petersburg, 1994. SPIE Vol.2259, pp. 605-608). Depending on the nature of the RD transformations taking place, they either form unique electrical, magnetic, tribological, corrosion-resistant or other advantageous properties to materials, or they may damage the material. It is absolutely vital to account for RD effects to assure the safety of nuclear power reactors, as well as to design and certify radiation-resistant materials.

In characterizing radiation exposures, parameters such as the number of displacements per atom and the rate of radiation damage accumulation are mainly used. Fine structure and spatial distribution of initially induced radiation defects are considered in the analysis to a much lesser extent. And, as a rule, the fast radiation-dynamic effects connected with propagation of shock and elastic lattice waves generated at the final stage of evolution of atomic collision cascades are ignored altogether.

The latter is particularly important for unstable (metastable) media with high stored energy in which, under intensive radiation exposures, fast phase transformations, self-propagating into the depth of the material, may be initiated (see [3], also: 4. Borodin S.N., Kreindel Yu.Ye., Mesyats G.A., Ovchinnikov V.V. et al. Pisma v ZhTF, 1989, v.5, b.17, 51-55; 5. Kreindel Yu.Ye., Ovchinikov V.V. Vacuum, 1990, V.42, N 1/2, pp. 81-83; 6. Ovchinnikov V.V., Erkabaev M.A. Transact. IX Int. Conf. on Rad. Phys. of Sol. (Sebastopol). Publ.: Moscow, 1998, pp.22-24, ISBN 58971-002-X). Here, an analogy may be drawn to the explosive crystallization of an overcooled liquid at shaking or throwing in a stone. In the absence of external actions, the lifetime of metastable media may be a matter of a few picoseconds to several geological periods (diamond is a typical example of a long-lived metastable state).

By comparing the characteristic lifetime of an atomic collisions cascade (t1~10-13 s) with the characteristic times of nuclear (t2~10-8 s) and chemical (t3~10-5 s) explosions, and bearing in mind that the characteristic thermal conductivity duration is R ~a×t1/2 (where a is the coefficient of temperature conductivity of material), it is easy to show that in the region comparable in size to a dense cascade region r0~50 Å a microshock wave may be generated only by exposure to radiation, since a×t11/2<<r0. In the case of a chemical explosion, the corresponding quasi-adiabatic region has macroscopic dimensions.

In prior investigations conducted by the authors of the Project (IEP UB RAS and RFNC), fast RD phase transformations have been detected in amorphous and crystalline metals and alloys by irradiation with neutrons and heavy ions. In some cases, re-crystallization (with change of their crystal structure type) was observed in the total volume of macroscopic samples. In others, fast processes of new phases segregation and long- and short-range atomic ordering took place in the whole volume of metal targets. In a number of cases, unique new electrical, magnetic, mechanical, and other properties of materials were obtained (see, e.g.: 7. Ovchinnikov V.V., Chernoborodov V.I., Ignatenko Yu.G., Nucl. Instrum. and Meth. in Phys. Res. B 103, 1995, 313-317; 8. Ovchinnikov V.V., Kogan Yu.D., Gavrilov N.V., Shtoltz A.K. Surface and Coating Technology, 64, 1994, 1-4).

Unfortunately, the physical mechanisms responsible for RD processes have not been thoroughly studied. The present Project will make ground-breaking progress in this field. Systematic investigation of the initiation and the mechanism of RD processes in model and engineering materials will be coined out, which will make extensive use of the unique facilities and expertise provided by the Project participants and foreign collaborators.

All the participating institutions represent the leading institutions in Russia in the field of designing and building unique research reactors (RFNC-VNIITF), charged-particle accelerators and other electrophysical equipment (IEP UB RAS and RFNC), investigation of radiation effects in materials (IEP UB RAS, RFNC, IMP UB RAS), designing of new radiation-resistant materials (IMP UB RAS). The RFNC is the leading center for nuclear weapons development in Russia.

The participating institutions have at their disposal unique modern facilities to generate all types of radiation, as well as novel, including original, analytical techniques. To implement the tasks set by the Project program, beside the researchers from the direct participating organizations, leading specialists from other renowned research institutions of Russia will be consulted, including those from the Joint Institute for Nuclear Research (JINR, Dubna), the Kurchatov Institute Research Center and others.

Anticipated results:

– fundamental laws governing RD processes in metals and alloys under irradiation with neutrons, heavy ions and fission fragments will be elucidated;

– information on the role of RD effects in changes of the properties of construction materials and radiation-resistant steels for nuclear and fission reactors in connection with the nuclear reactors safety problem;

– methods to improve the electric and mechanical properties of soft magnetic materials (transformer steels, nanocrystalline and amorphous soft magnetic materials) by ion-beam treatment resulting in substantial reduction in losses for reversal of magnetization at medium and high frequencies will be developed;

– methods of modifying the electrical resistivity (r) and the temperature resistance coefficient (TRC) of metal alloys, e.g. in the systems of Fe-Pd-Au and Fe-Ni, by high-current beams of fast ions will be developed to create unique parameters of electrical resistivity (unattainable by other treatment methods);

– radiation effects on magnetoresistive properties of Fe/Cr, Co/Cu superlattices with giant magnetoresistive effect will be determined;

– methods of initiating RD phase transformations (atomic disorder)→(long-range atomic order) in metal alloys under temperatures below the “diffusion defreezing” thermal threshold will be developed;

– methods of initiating RD phase transformations of diffusion-free type at anomalously low temperatures will be investigated;

– results of investigation of lattice (phonon) and electronic excitations using the Moessbauer effect directly in the course of ion irradiation (in situ) will be generalized.

The fundamental knowledge gained will be utilized to predict variations in properties of materials (including nuclear construction materials) undergoing various types of irradiation, and to develop innovative methods of ion-beam modification of anomalously deep subsurface layers in materials to generate unique properties, including modifications using plasma immersion ion implantation. The use of RD effects to increase the depth at which materials may be modified has significant economic advantages, as compared with the currently used combinations of ion implantation with other methods (an example may be ion-assisted deposition).

The Project affords the opportunity to redirect the efforts of nuclear weapon designers participating in the project to peaceful civilian applications connected with assuring nuclear safety and development of basically novel radiation technologies for materials processing. It is also aimed at integrating the scientists involved in the project into the larger world scientific community and supporting fundamental and applied research. In general, the proposed project supports Russia’s transition to a market economy to meet the civilian needs.

The scope of the project is determined by the need to solve a comprehensive multi-tasked experimental problem:

– investigation of the mechanisms of RD processes in metastable metals and alloys (In more than ten specially selected objects: alloys of systems iron-nickel, iron-manganese, iron-aluminum, iron-silicon, iron-palladium-gold, ultrafine-grained Fe and Cu, amorphous and nanocrystalline electronic materials, Fe/Cr and Co/Cu superlattices with giant magnetoresistive effect, etc.), as well as in a number of structural materials used in nuclear power plants, for various irradiation types and depending on conditions (parameters) of irradiation: E, M, dФ/dt, Ф, T (where E, M, dФ/dt and Ф are energy, mass, flux and fluence of ions, and T is target temperature), and the parameters and structural state of the irradiated media.

Solving of this problem requires, in the first place, fulfillment of a number of particular analytical tasks, the most labor-intensive of which are the following:

– studies using the methods of field ion and transmission electron microscopy of the structure and distribution of radiation-induced defects in the investigated materials with regard to the type and conditions of irradiation, including the structure and distribution of ”frozen” clusters (dense cascade regions that are source of RD effects formed at 77 K); investigation of changes in phase composition, and atomic and magnetic structure of reference and engineering materials undergoing RD transformations by X-ray diffraction, field ion and transmission electron microscopy, Moessbauer effect and several other methods; and studies of the correlation between microstructure and macroscopic properties of such materials under various types of irradiation with varying exposure parameters.

In fact, the latter study envisages establishing experimentally multiparametric dependences Pi=Pi(E, M, dФ/dt, Ф, T) and S=S(E, M, dФ/dt, Ф, T) for the investigated materials, accounting for differences in their initial states, where Pi represents measured properties (electrical, magnetic, mechanical), and S is some unified parameter characterizing the structural state (e.g., if phase composition changes only, S may stand for the content of the phase formed under irradiation). It is clear that the Project comprises an extensive and labor-intensive set of tasks. Therefore, careful planning of the experiment will be required to reduce the number of measurements.

The methodology and technical approach feature the following main aspects. For comprehensive analysis of the role of RD effects, various types of corpuscular irradiation will be used, with the particle beam parameters, as well as the irradiated media temperatures and properties varying over a wide range. High-current continuous, repetitive-pulsed and fine-focused scanning ion beams will be used, as well as combined electromagnetic and ion irradiation (with gradual replacement of the ion beam power by electromagnetic irradiation, from 0 to 100 percent) in order to differentiate the roles of thermal and RD effects.

The Project participants and collaborators have at their disposal unique research reactors and accelerators (E = 1–5×108 eV) to meet this task, along with the available equipment of standard and original analytical methods and techniques for condensed matter investigations (X-ray structure analysis, neutron diffraction analysis, Moessbauer effect, SIMS, ESCA, resistivity and magnetic measurements, etc.), and the original analytical methods and techniques for condensed media (surface and volume) investigation including the Moessbauer effect and resistivity measurements in situ (directly during irradiation), a complex for neutron irradiation and investigation of the physical properties of materials at cryogenic temperatures (77 K), etc.

The foreign collaborators from the Forschungszentrum Rossendorf, Institute of Ion Beam Physics and Materials Research (FZR/FWI, Germany), will carry out the following tasks:

– complementary experiments under the Project at FZR/FWI using different types of ion accelerators, including an apparatus with a scanning fine focused ion beam of high current density;


– sample analysis using the facilities for surface investigation available at FZR/FWI, including use of high-energy ion beam analysis.

They will also carry out an independent assessment of the results in the course of work, and participate in working meetings and seminars under the Project. Joint use of the research results is anticipated, with joint patenting, if required.


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